1. Technical Field
The present invention relates to a gas-filled discharge tube, and more specifically to a gas-filled discharge tube used to control voltage in a gap switch for activating a laser apparatus, a sharpener gap switch, an arrester, etc.
2. Description of the Related Art
A discharge tube is used as a gap switch for activating a laser apparatus, a sharpener gap switch, an arrester, etc. As the discharge tube as described above, a discharge tube filled with an inert gas is well known, in which two discharge electrodes are arranged so as to be opposed to each other within and on both sides of an insulated cylindrical casing, as shown in FIG. 1. In this conventional gas-filled discharge tube, a cylindrical casing 1 is airtightly sealed by two metal end plates 3A and 3B' each formed integral with a discharge electrode 2A or 2B on both sides of the casing 1. Further, two gas-sealing tubes 4A and 4B are airtightly passed through the metal end plates 3A and 3B and the discharge electrodes 2A and 2B into the casing 1, respectively.
The gas-filled discharge tube as described above with reference to FIG. 1 can be manufactured by evacuating the internal space of the casing 1, introducing an inert gas into the casing 1 through the gas sealing tube 4A, and crushing an end of the gas sealing tube 4A into a flat shape by applying pressure between both the side surfaces of the gas sealing tube 4A (as disclosed in Japanese Published Unexamined (Kokai) Utility Model Application No. 3-24290 or Patent Application Nos. 3-141574 and 5-7032, for instance).
The gas-filled discharge tube is used in various fields, and thereby a small-sized tube is often required according to the use. In the conventional gas-filled discharge tube, however, since the diameter of the gas sealing tube 4A must be reduced with decreasing size of the discharge tube or the casing 1, when the casing 1 is evacuated (before the gas is introduced into the casing 1), the evacuation efficiency is low even if a vacuum pump of high performance is connected to the gas sealing tube 4A. As a result, there exists a problem in that impurities sticking onto the inner surface of the cylindrical casing 1 and the discharge electrodes 2A and 2B cannot be removed sufficiently, so that the discharge characteristics of the manufactured gas-filled discharge tube deteriorate with the passage of time. On the other hand, since it takes relatively a long time to perfectly remove the impurities sticking onto the inner surfaces of the discharge tube, tile productivity is inevitably lowered.